This research project investigates the role of cyclic nucleotides in regulating circadian and light-induced retinomotor movements and photoreceptor shedding in the green sunfish, Lepomis cyanellus. We will characterize the contributions of light and circadian rhythms to retinomotor movements of rods, cones and retinal pigment epithelium (RPE) over a 24 hour cycle plus 4 hours by quantitating retinomotor position and phagosome numbers at 2 hour intervals in constant light, constant darkness, and after 1.5 hr exposure to light or dark just prior to fixation. We will ascertain whether there are circadian changes in retinal and RPE cyclic nucleotide levels in constant darkness by radioimmunoassay. We will compare the effectiveness of various phosphodiesterases in inducing retinomotor movements in cultured retinas. We will determine whether cyclic GMP induces retinomotor movements in vitro. We will determine whether injected cyclic AMP blocks circadian or light induced post-dawn photoreceptor shedding in fish or rats. We will ascertain whether circadian retinomotor movements occur in retinas cultured in constant darkness to see if the circadian cues are intrinsic to the retina. We will determine whether we can induce retinomotor movements in the absence of light or circadian cues by experimentally altering cytoplasmic calcium levels with the ionophore A23187. We will try to localize sites of calcium sequestration in retinas with an ultrastructural cytochemical stain for sarcoplasmic reticulum.